Tanning with tetrakis-



United States Patent TANNING WITH TETRAKIS-(HYDROXYMETHYL) PHOSPHONIUM CHLORIDE Edward M. Filachione, Philadelphia, Pa., assignor to the United States of America as represented by the Secretary of Agriculture No Drawing. Application March 22, 1955, Serial No. 496,086

A non-exclusive, irrevocable, royalty-free license in the invention herein described for all governmental purposes, throughout the world, with power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to the tanning of hides and the manufacture of leather.

An object of this invention is to provide novel and improved processes for tanning hides. Another object is to provide leather having new and desirable properties.

The term hides," as used herein, includes all animal skins that are tanned commercially, such as cowhide, horsehide, calfskin, pigskin, sheepskin and fur skins.

The bulk of commercial tannage is by use of vegetable tannins and chrome tannage.

Vegetable tanning is slow and tedious, requiring many steps and several weeks of time.

Chrome tannage is quicker but more expensive. Both produce leathers having pronounced discoloration; hence, neither is suitable for the production of white or lightcolored leathers. Both require a low pH (acidic condition); hence the lime commonly used in preparing skins for tanning must be completely removed or neutralized.

According to the invention, a quick and thorough tannage at high or low pH, yielding leather having substantially no discoloration, is achieved by treating hides with tetrakis-(hydroxymethyl) phosphonium chloride (hereinafter abbreviated as THPC). Only a small percentage of THPC is required for satisfactory tannage and it may be applied as an aqueous solution or dissolved in an organic solvent, such as a lower aliphatic alcohol or ketone.

In general, the hide is prepared as for conventional tannage. THPC readily tans hides that have not been pickled and that contain residual lime from the liming step. The pH at which THPC tans best is near the isoelectric point of the hide. This will vary somewhat with different kinds of hide and with the type of pretanning treatment given the hide. In general it is in the range of pH 4-6 and the optimum pH for THPC tannage is usually in the range 3-9. At lower pH values tannage is considerably slower while at higher values some of the THPC may be lost through reaction with the alkaline reagent. Usually, however, satisfactory results may be obtained throughout the pH range of about 2-12.

The temperature of the tanning bath may be varied widely up to the shrinkage temperature of the hide being treated. Faster tannage is obtained at elevated temperatures. Even at ordinary room temperature, however, very rapid tannage isobtained so that usually there is little advantage in applying heat to the tanning bath. Even at 15-20 C. tannage is usually complete in 1-2 hours.

Only a small amount of THPC is required for tannage, usually about 15% based on the dry weight of the hide. When the tannage is complete, absorption of THPC substantially ceases. of time or high concentrations of THPC do not result in significantly higher degrees of tannage or greater absorption of the reagent. On the other hand, untanned or partially tanned hide, as well as leathers tanned by conventional processes, have a powerful afiinity for THPC and will absorb it from even very dilute solutions. This is a great advantage since it enables the tanner to use an initially strong tanning bath and yet, after it is progressively depleted through use, to exhaust the bath to substantially zero concentration of THPC before discarding it.

The following examples illustrate several embodiments of the invention. 1

The abbreviation Ts stands for the shrinkage temperature of the hide or leather as determined in a hot water bath.

EXAMPLES l-lS The cowhide used in these examples was the commercial white hide obtained after the usual liming and unhairing stages of beamhouse processing. The hide was stored in a cold room after pickling with salt and hydrochloric acid. Prior to use the pickled cowhide was depickled by immersion in sodium bicarbonate, then thoroughly rinsed in water. Generally 15 grams (on a dry weight basis) of the cowhide was treated with ml. of an aqueous buffered solution of tetrakis-(hydroxymethyl) phosphonium chloride. Gentle agitation of the cowhide under treatment was accomplished by carrying out the re action in a bottle which was rolled on a jar mill. The bottle cap contained a vent, above the liquid level, to prevent build up of pressure which was particularly noted in Examples 6, 8, 9, 14, and 15. The calfskin used was pickled calfskin obtained from a commercial tannery. After the materials had been treated with THPC they were rinsed thoroughly in water and air dried. All the treatments, except the treatment of Example 10, gave white, firm, flexible leather products.

Pertinent data are shown in the following table.

Treatments involving extended periods Table-Tanning with THPC Initial Ooncn. of

05 Hour 1 Hour 2 Hours 4 Hours 24 Hours THPC, Percent pH pH None Phosphate tate Phosphate. Bicarbonate".

. o Phosphate. Lime Phosphate do do Bicarbonate... Phosphate.

mcngomcnumorgecnmpsmmm Analysis, percent phosphorus, of treated cowhide: after 1 hr. 0.23% (0.26% M. F. B.); after 2 hrs., 0.31% (0.34% M. F. B.); alterhrs. 0.37%

(0.41% M. F. B)

b Analysis, (0.74% M. F. B.

a The weight gain of the treated calfskin was approximately 36%.

EXAMPLE 16 A sample of cowhide which had been tanned with tetrakis-(hydroxymethyl) phosphonium chloride as in Example 3 above (Ts=79 C.) was treated with a concentrated solution (30% solids or 105 Barkorneter) of sulfited quebracho extract. After two days the vegetable tannin had completely penetrated the cowhide, and the shrinkage temperature of the cowhide under treatment was elevated to 90 C. After rinsing in water the treated cowhide dried to a leather resembling sole leather.

EXAMPLE 17 I ercent phosphorus, of treated cowhide: after 1 hr. 0.34% P (0.38% M. F. B.); after 2 hrs, 0.43% P (0.48% M. F. B.); after 4 hrs. 0.67% I (THPO). Hence, it appears probable that when THPC is used as a tanning agent in an alkaline solution, the active agent is THPO. In any case, I have found that THPO is a tanning agent and, in alkaline solutions, is equivalent to THPC. In acid solutions it appears to be less reactive than THPC, though still effective.

I claim:

1. A process for tanning hides comprising treating the hides with tetrakis-(hydroxymethyl) phosphonium chloride at a pH of about 2 to 12.

2. A process for tanning hides comprising treating the hides with tetrakis-(hydroxymethyl) phosphonium chloride at a pH of about 2 to 12, and then retanning with vegetable tannin.

3. A process for retanning leather comprising treating the leather with tetrakis-(hydroxymethyl) phosphonium chloride at a pH of about 2 to 12.

References Cited in the file of this patent UNITED STATES PATENTS 2,668,096 Reeves et a1. Feb. 2, 1954 

1. A PROCESS FOR TANNING HIDES COMPRISING TREATING THE HIDES WITH TETRAKIS-(HYDROXYMETHYL) PHOSPHONIUM CHLORIDE AT A PH OF ABOUT 2 TO
 12. 